Selective Separation of Hexachloroplatinate(IV) Dianions Based on Exo-Binding with Cucurbit[6]uril

The recognition and separation of anions attracts attention from chemists, materials scientists, and engineers. Employing exo-binding of artificial macrocycles to selectively recognize anions remains a challenge in supramolecular chemistry. We report the instantaneous co-crystallization and concomitant co-precipitation between [PtCl6](2-) dianions and cucurbit[6]uril, which relies on the selective recognition of these dianions through noncovalent bonding interactions on the outer surface of cucurbit[6]uril. The selective [PtCl6](2-) dianion recognition is driven by weak [Pt-Cl...H-C] hydrogen bonding and [Pt-Cl....C=O] ion-dipole interactions. The synthetic protocol is highly selective. Recognition is not observed in combinations between cucurbit[6]uril and six other Pt- and Pd- or Rh-based chloride anions. We also demonstrated that cucurbit[6]uril is able to separate selectively [PtCl6](2-) dianions from a mixture of [PtCl6](2-), [PdCl4](2-), and [RhCl6](3-) anions. This protocol could be exploited to recover platinum from spent vehicular three-way catalytic converters and other platinum-bearing metal waste.

Automated summary

This study presents a new method for selectively recognizing anions in supramolecular chemistry, achieved through the selective recognition of [PtCl6] (2-) dianions on the outer surface of cucurbit[6]uril using weak hydrogen bonding and ion-dipole interactions. The method demonstrates high selectivity among seven metal chloride anions.